Evolutionary Biology
Exam II, Fall 2011
Part II
K E Y__________
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Your Name
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Lab Time & Day
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TA Name
B. Suppose you were asked for only one criterion (Do not give more than one!) that distinguishes the
following pairs of organisms from one another, what would you say? Write out complete sentences.
(2 pts. each)
1. Prokaryotes vs. Protista
Protista have all of the eukaryotic cell characteristics (mitochondria, ER, Golgi, vesicles,
nuclei, etc) and Prokaryotes lack them.
Prokaryotes have one circular chromosome & Protista have multiple linear chromosomes.
2. Cyanobacteria vs. all other bacteria.
Chlorophyl a present in cyanobacteria
2 photosystems
Release O2 as waste product of photosynthesis
3. Angiosperms vs. gymnosperms
Flowers in Angiosperms
Ovary in Angiosperms
4. Viruses vs. all other organisms
Viruses are “non-living” - non-cellular
Consist only of nucleic acid and protein coat
Viruses can’t reproduce without host organism
5. Sporophytes vs. gametophytes
Sporophytes produce spores.
2n
(Gametophytes don’t; they produce gametes.)
n
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C. Comment on the validity of these statements, giving sound reasons for your belief. (2 pts. each)
1. It is likely that life arose several times in earth’s history.
Not true. Life probably only evolved once since the biochemistry of all
organisms is roughly similar.
e.g. Nucleic acids are structured in a basically similar way.
2. The endosymbiotic hypothesis is not adequate to explain all aspects of the origin of eukaryotic cells.
Correct. It is not adequate. It is only adequate to explain that chloroplasts
and mitochondria were probably once bacteria. It attempts to explain that
flagella might have been spirocheate bacteria. It does not explain where the
nuclear membrane, Golgi apparatus, endoplasmic reticulum membranes
came from.
3. The butterfly eye and the vertebrate eye are a good example of divergent evolution resulting in
homologous structures.
Not true. These are good examples of analogous structures arising by
convergent evolution.
4. There has been a co-evolution of Australian rabbits and the myxoma virus.
True. The Australian rabbit was originally easily killed by the virus. Tests
have shown that the rabbits are now largely resistent and now the virus
is much less lethal. Both virus and rabbits have evolved.
5. Kin selection and sexual selection are virtually identical.
Not true. Kin selection is where close relatives carry the same genes as one
another and are thus likely to behave altruistically toward one another.
Sexual selection refers to the fact that individuals of the same sex (usually
males) compete for reproductive rights, either by contests (who is biggest,
strongest) or most attractive (female choice). The winner gets to mate.
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D. In the News
In Sunday’s paper The Buffalo News. March 30, 1997, the following article appeared.
BUGS WORK UP RESISTANCE
Crop pests may become resistant to some insecticides with surprising ease, a new study
suggests.
Pesticide manufacturers like to use toxins from a common soil bacterium in
their products because the chemicals kill bugs but don’t appear to harm
people. New research examining diamondback moths, however, has found
that just one gene like a key that opens several doors, can give the insects
resistance to at least four different toxins.
Prior to these results, most agricultural experts assumed that to develop
resistance, bugs would need a separate genetic mutation for each different
chemical.
“These findings suggest that pests may evolve resistance to some groups of
toxins much faster than previously reported,” the researchers report in the
current issue of Proceedings of the National Academy of Sciences.
The experiments were conducted by scientists from the University of
Hawaii, the Biotechnology Research Institute in Montreal and Clemson
University.
How would a Lamarkian explain such results? (5 pts.)
A Lamarkian would argue that the environment induced the moths to adapt
to their environment. Thus, the environment acted directly on the genetic
constitution of the moths and produced an appropriate gene, making them
more successful. This is Lamarck’s idea of evolution by “Acquired
characteristics”.
How would a Darwinian explain such results? (5 pts.)
Darwinian’s would explain the result via natural selection. They would argue
that the moths had variations in their ability to tolerate the toxins. Some were
lucky enough to have a gene that allowed them to tolerate several toxins. Those
that had the gene would survive and bear young with their same genetic
constitution. These would rapidly replace those that lacked the gene and were
not tolerant.
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2. Also in the Sunday, March 30, 1997th Buffalo News, we read that scientists from Yale have shown
that some people have an ability to taste a chemical called propylthiouracil (PROP) and others can’t.
A test is administered by having people put a piece of paper laced with PROP in their mouths for a
few seconds. Some people taste a strong bitter flavor, other people taste a mild bitter flavor, and still
others taste nothing at all. This appears to be a genetically determined trait that produces three types
of tasters. Researchers think it depends upon the number of special taste buds on the tongue.
Answer the following questions with explanations. (10 pts.)
a. Is this likely to be a polygene trait? Why?
No, it is not likely to be a polygene trait. There are only three phenotypes expressed.
Polygene traits produce many more phenotypes (often producing a normal curve in
frequency distribution of the trait).
b. Can we distinguish between complete dominance, incomplete dominance, and co-dominance in the
expression of the trait?
Since there are three phenotypes; one of which is intermediate (mild tasting ability),
it is either incomplete or co-dominance, not complete dominance. We cannot tell
the difference between incomplete or co-dominance except at the molecular level.
c. If 100 people were tested and we found the data shown below, would this suggest that the population
is in Hardy Weinberg equilibrium? Super tasters =16%, medium tasters =48%, and non-tasters =36%
Supposing tasting is dominant (T) - then Super tasters (TT), Medium tasters (Tt) and
Non-tasters (tt)
then q2 = .36 and q = .6 and p = .4
p2 = .16 and 2pq = 2(.4 x .6) = .48 and q2 = .36
Thus, the population seems in equilibrium.
d. If the above were true, would you expect either genetic drift or selection to play a strong role in
determining the proportion of individuals with the various tasting abilities?
If the Hardy-Weinberg equilibrium is in effect, then natural selection is not
operating but genetic drift will be.
e. Suppose that tasting is a dominant trait, if two medium tasters were to have children, what types and
proportions of phenotypes would you expect?
Tt x Tt = 25% TT tasters, 50% tasters
25% non-tasters
So 3:1 ratio of tasters to non-tasters.
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E. Origins of Species (5 pts. each)
1. Using examples, discuss differences between allopatric and sympatric speciation. Why is sympatric
speciation more common among plants than animals?
Allopatric speciation occurs when two populations become geographically separated and
then become distinct species by developing reproductive isolating mechanisms.
e.g. - most species are believed to have evolved this way.
Sympatric speciation can occur when two species develop from a single ancestral species
while living in the same geographic area.
e.g. - many parasites may have evolved this way by specializing on their particular host.
Sympatric speciation is more common in plants because species hybridize frequently to
“instantly” produce a new species in the same geographical area.
2. Discuss the biological species concept and three of its problems.
A biological species is a population of organisms that share the same gene pool and are
relatively isolated from other such gene pools. i.e. - two different species will not
normally successfully reproduce with one another.
Problems: 1.) This definition doesn’t work for asexual species.
2.) This definition doesn’t work for fossils.
3.) This definition doesn’t work for evolving species (phyletic species).
Gradual changes occur and can’t tell when one generation is sufficiently
different that they could not have breed with previous generation.
4) This definition doesn’t work well for ring species
Gradual changes occur over a large area and it is difficult to tell when one
population is sufficiently different that they could not breed with
neighboring populations except at their extreme ends.
( 5) If one were using a morphological definition of a species than polymorphic
and sibling species are difficult to discern, but if breeding is the criterion
then the biological species definition works fine for these groups.)
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